Cellulose ether is commonly used for commercial purposes to prepare films such as gastric hard capsules and enteric hard capsules.
The preparation of cellulose ether involves alkalizing cellulose pulp by contacting it with sodium hydroxide; etherifying the alkalized cellulose pulp using methyl chloride to form cellulose ether; washing the cellulose ether to reduce sodium chloride content in the cellulose ether; drying the washed cellulose ether to reduce water content, and pulverizing the dried cellulose ether. The sodium chloride as a product of a reaction of the sodium hydroxide used in the alkalizing of the cellulose pulp with the methyl chloride used in the etherifying the alkalized cellulose pulp and hydrochloric acid used in hydrolyzing the cellulose ether may remain in a final cellulose ether.
According to existing technologies, a film prepared using a cellulose ether solution prepared from cellulose ether with a high sodium chloride content (for example, greater than about 0.3 wt %) may undergo quality degradation due to salting out and a haze on a surface thereof when stored at a predetermined temperature and a humidity condition for a long time.
U.S. Pat. No. 6,294,008 discloses a method of washing an increased number of times in preparing cellulose ether to reduce a sodium chloride residue to about 0.3 wt % or less. However, the increased number of washings in this method may increase manufacturing costs and wastewater efflux, thereby raising environmental concerns.